Chemical plating



Patented Aug. 8, 1939 UNITED STATES PATENT OFFICE CHEMICAL PLATING NDrawing. Application October 11, 1934, Serial No. 747,885

Claims.

One principal object of this invention is to combine a metal cleaningmaterial with chemical plating material in a dry form with a means ofdispensing and application which affords the 5- advantage ofguaranteeing to the user a complete non-scratching plating process.

A second object is to utilize a chemical plating material in which ifdecomposition sets in, the resulting decomposition product retains thenon-scratching characteristic and further provides a mild abrasive as anadded ingredient of the cleaning material.

An additional object is the prevention of decomposition by adding meansto the compounded material which prevent the reflective redistributionof light rays and consequently the decom position of light sensitiveingredients in the chemical plating material.

A further object is the providing of a handy portable means for quickchemical plating of objects with various metals such as copper, silver,gold etcetera, the applicator being retained in the dry form until itshall be desired to be used.

In demonstration of the above objects, and by 5 way of example,following formulas are to be given, of novel nature and contributing tothe art of metal finishing and preservation.

As is well known in the electroplating art, there are a considerablenumber of ways in which 30 certain metals such as silver, gold, nickeland copper may be deposited by wet contact with a plating solutionthrough immersion, or rubbing in paste form.

Accepted theory for such action is that salt solutions of metals to bedeposited will form a metallic coating provided the electromotivepotential of a solution is rated higher than that of the base metal onwhich the coating is to be laid. Coatings made by simple immersion or 40rubbing, though usually only a few milli-microns thick have,nevertheless, a certain commercial utility.

Compounding of contact plating pastes and solutions with mild abrasiveswhich clean the surface to be coated in addition to providing anelectro-depositing action, is old and well-known in the art, and is notclaimed as novel in the invention to be described.

A typical formula for immersion or contact 50 plating with silver isherewith given, in order to present a clear exposition of the invention.A quantity of chloride of silver is first dissolved in a saturatedsolution of potassium or sodium cyanide. The proportions may vary withthe 55. desire of the compounder, and the requirements of the material.A useful ratio of the two respectively, is one to three, which providesa quantity of free cyanide which not only accelerates the plating actionbut also aids in quick removal of oxides, sulfides and other compounds 5from the surface of the metal to be coated.

At this point the cleaning compound is added. By example, whiting orprecipitated chalk is mixed in with the solution. As is well known, thismaterial is calcium carbonate, non-soluble 10 in pure water, but goinginto solution in the presence of carbon dioxide. The quantity may equalby weight that of the metal salts and is not critical in efiect.

The addition of a small amount of carbon bi- 16 sulphide or carbondisulphide may be madeat this point. Its presence provides a control forthe grain or crystal size of the deposited silver, tending to cause suchformation to yield a bright mirror finish. Further, a quantity of thesul- 20 phide will break down releasing sulfur dioxide and yielding asmall amount of carbon dioxide for taking some of the calcium carbonateinto the solution, the net effect having a tendency to stabilize thesilver salt, and delay decomposition, especially if the mixed materialhas to Withstand heat. The formed fine emulsion of the carbon disulphideappears to retard crystal size and growth, but an oversupply will yieldan undesired dark deposit.

The formula is now ready for the use of ad'-v dition agents utilized formasking the light transmission throughout the mixed material which upuntil this point is a grayed white, the salt solu tion being transparentand the whiting providing a high degree of light transmission by particle reflection.

Carbon in the form of lampblack or in precipitated colloidal form is nowadded. The propor tion of such carbon is not critical except that 40sufficient is used to cover against light. This material is not only amild abrasive, chemically inert to the ingredients of the solution,possessing unique hiding power against light transmission which woulddecompose the silver salts, but also adds absorptive power to theformula against impurities and undesirable quantities of sulphides.

As a furtherhiding and homogenizing means small quantities of solubleaniline dyes, such as the rosanilines are added to the solution, to as-L sist in light protection, and to initiate a binder characteristic inthe paste being formed. These may also take the form of thenaphthalene-diazoacidic dyes, either sulfo, carboxylic, amino orhydroxyl types, or the naptho-sulfonic groups;

napthionic crocein; or the Neville-Winther azo dyes. Preferably suchdyes are soluble in water, or else adsorbable into the carbonates. Asufficient quantity of dissolved sugar of the nongranule-forming type,such as levulose sugar may be added for providing a binder, althoughthis latter may be found not necessary in practise. The aniline ispreferably of the violet-blue-green end of the color spectrum forobvious reasons.

A summary of the ingredients of the described formula to the presentstate is now given:

a. Electroplating materials I). Cleaning materials 0. Brightening agentsd. Light hiding substances e. Binder materials The mixture as nowdescribed is in the form of a semi-liquid paste, and being thoroughlymixed, is ready for combining with the applicator material.

In the following silver plating formulas, fresh precipitate of silverchloride, described preceding, is intended to be used.

Mix into a water paste the following; by weight:

Parts Silver chloride 2 Calcium carbonate (whiting) 3 Sodium chloride(C. P. salt) 2 Potassium carbonate 4 If for any reason, the above groupis not sufficiently non-poisonous, the following is recommended:

Parts Silver chloride 1 Argol (potassium bitartrate) 2 Sodium chloride(C. P. salt) 2 Calcium carbonate (whiting) l The samples of variousformulas are stated in order to suggest a wide utility for my invention,the article of which may include them in combi nation with the additiveingredients noted here- Sheets or continuous strips of non-siliceouspaper, fiber or cloth are coated with the paste, or dipped in it, andallowed to dry. These may be of Vegetable fiber such as cotton linters;or of artificial form, as for example the material known commercially ascellulose sponge, and that known as Japanese tissue. No claims are madefor a specific method of coating or preparing such applicator material,in that machines for like purpose are commonly used for many similarprocesses. One process employs a roller which. picks up a unit quantityof liquid and lays it on the continuous skein of such fibrous material,excess liquid being removed by a straight edge or knife. Other sheetingprocesses work directly from pulp to final sheet form, all ingredientsbeing in the pulp tank.

In the latter type of process, all the materials to be included in theapplicator are mixed in the pulp tank, and a continuously moving screenof wire or felt picks up the pulp, passing through drying boxes andwringer rollers, as is commonly known in Fourdrinier paper makingmachine practise, with equipment known to the trade as Harper, Yankeeand others.

Low temperature drying means are used, to avoid excessive decompositionof the metallic salts included in the materials. The copper or brasswire screening of such a machine is coated with the metal of the saltsolution being worked either before the pulp is started flowing, or elsethe wire is allowed to be coated by the pulp material itseli,whereafter, in a short time, further deposit ceases.

Finished sheeting may be crepe or corrugated, as desired. To facilitateporosity, freezing of the sheet prior to drying may be utilized. Cottonrag stock, or cellulose fiber mixed with wool, such as is the bases forunsized blotting paper filter paper and filter mass, are acceptable pulpbases for my process, the only restriction being that the material shallbe non-siliceous or non-scratching. The resistivity of the cellulosefiber to chemical action determines that the pulp shall contain a fairlyhigh percentage of cellulose fiber material. Further the power ofattraction to metal salts and bases in solution of cellulose, gives aholding power to the base, which increases the efficiency of my process,Absolutely pure cellulose fibers may be obtained by boiling cellulosepulp with dilute sodium hydroxide, washing, and moist exposure tochlorine gas.

Such sheets may be transversely cut or per-- forated to facilitateremoval of unit quantities from the whole by the user. The final articleconsists of a roll, or stack of impregnated sheets, in dry form. In thecase of the silver formula described preceding, the material in the rollwould in time deteriorate because of the action of light rays, andespecial novelty is claimed for the peculiar protective characteristicof my article.

The technique of my combinations may be applied to other than silverplating means, and it is my purpose to claim the features of novelty asapplicable to contact plating processes since these features embrace ascope of use beyond the simple coating of silver, for example.

The completed dried article is boxed, sealed and stored until requiredfor use. The operator has only to moisten the article with a liquidwhich has the power of putting the metallic salts into solution. In thedescription of the contact silver plating process given preceding, sucha liquid is ordinary water, or distilled Water. Other liquids andsolutions may be used, as for example, a sensitizing solution ofpotassium or sodium cyanide.

Now it should be clearly understood that the types of ingredientsdescribed herein may be mixed with the fibrous carrier in a mannersimilar to commonly known paper manufacture, wherein a continuous skeinis drawn through a pulp tank containing all of the ingredients includingthe carrier fibers, the materials being somewhat more intimately mixedthan in the first described method. The pulp drawn out on the skein isformed in a layer of uniform thickness, dried and boxed, just asdescribed preceding wherein the fiberbase is separately coated.

The following formulae describe the extension of my invention to copper,tin, and gold plating, as examples of the application and use hereindescribed.

Stannous chloride, 2 parts; cream of tartar 4 parts (by weight)dissolved in water, will deposit tin on brass and other metals if theapplicator or article is kept hot, at or near the boiling point ofwater. Zinc filings or dust, mixed with the above and intimately mixedwith the fibers of the applicator along with the chloride and tartrate,accelerate the action.

Cream of tartar 3 parts; 1 part carbonate of copper in a water solution;mixed slowly with calcium carbonate (whiting) until chemical actionceases; yields tartrate of copper, which dissolved in part caustic soda,and part potassium cyanide solution, provides a contact copper platingmeans for zinc, brass and other objects. Rubbing action may becontinued, at room temperatures until a deep red color of the copperdeposit is discernable.

For iron or steel objects to be copper coated quickly, equal parts ofcommercial sulfuric acid and copper sulfate dissolved in warm water,mixed with lampb-lack or similar inert cleaner agent, and combined withthe fibrous applicator material yields a good, adhering coat, butcontinuation of the process too long causes granules and flakes to form.

Metals to be gilded are first coppered, and heated in boiling water. Onesolution for gold plating them is made with potassium cyanide 2 partsand chloride of gold 1 part, in water. The quantity of free cyanidepresent, determines the speed at which gold plating is accomplished andit may be increased 5 to 10 percent, in practise, without disturbing theother factors. Three parts of water, 3 parts of calcium carbonate andoz. cream of tartar, with the above, forms a proper mixing paste for theabove combination, which with the fiber applicator, provides anexceptionally handy means to perform the work.

Chemical deterioration of these solutions is slow, and properlyprotected against light, in the dry form, in the applicator, asdescribed in this specification, combined with protective and cleaningagents, the resulting commercial article has a wide spread utility. Themaintaining of lamp reflectors in constant service, such as inlighthouses, airport beacons, automobile headlamps, the quick spotcleaning and surface repair of jewelry, cutlery, and metal fittings ofevery nature, under normal and special service conditions wherecorrosion destroys not only beauty, but also utility; is the main objectof my invention in providing my combinations of portable andnon-technical means whereby these services are supplied.

I claim:

1. A contact plating applicator comprising, a light-sensitive metallicsalt capable of contact deposition, a cleaning agent, a light hiding orabsorptive means and a paper in which said salt, said agent and saidmeans are impregnated.

2. A metal polishing and plating article comprising a cellulose fiberbase, a light-sensitive metal salt capable of contact deposition, acleaning agent capable of removing atmospheric oxides, a lightprotective means combined with said agent, said fiber being impregnatedwith said salt, said agent and said means in finely divided dry form.

3. A metal polishing and plating article comprising a cellulose fiber, ametallic salt capable of contact deposition, and a cleaning andprotective compound composed of a carbonate and colloidal carbon in dryform.

4. In the chemical plating art, in combination, an article compounded ofa non-siliceous fiber, a metallic salt capable of contact deposition, acarbonate, a soluble sugar, and carbon in finely divided form, thecompound forming a means of a cleaning and chemically plating of aconductive surface.

5. In the electro-deposition art, in combination, a conductivelight-sensitive metallic salt solution and suspended colloidal carbon insaid solution acting also as a deoxidizing agent.

DANIEL C. WILKERSON.

